1. Field of Invention
The invention relates to an electronic computer capable of exchanging blocks of data (records) between the working memory of the computer and a peripheral unit which performs the functions of a high-capacity external memory, such as, for example, a magnetic disc or drum unit.
2. Description of the Prior Art
An arrangement adapted to transfer blocks of data to (or from) the working memory is known which is based on the interruption of the program being executed. Generally, this is called direct multiple control (DMC). This arrangement utilizes a control program and a control circuit which are adapted to transfer data from the external memory to the working memory. The central unit has the task of initiating the transfer by indicating to the DMC program the initial and final addresses of the block of data to be transferred. The DMC will interrupt the working of the current program, usually for four machine cycles, whenever the peripheral unit is ready for the transfer of data. At the end of the transfer of each individual word, the central unit resumes execution of the interrupted program. When the transfer of the entire block of data has been completed, a suitable signal provides for inhibiting the DMC from further interrupting the central unit.
The disadvantage of this system is due principally to the slowness of the transfer, inasmuch as at each interrupt there is transferred a single word while four machine cycles are executed. Moreover, during these four cycles, the central unit is given over to the transfer and therefore substantially delays the program being executed.